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Colon: want to learn more about it?

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Colon

The colon forms part of the large intestine and extends between the caecum and the rectum. It is about 1.5 meters in length and consists of four parts:

  • ascending
  • transverse
  • descending
  • sigmoid colon

You can recognize it easily through several distinct morphological features like semilunar folds and pouches called haustra. In addition, taeniae coli are specific to the colon together with appendices epiploicae. Histologically, the mucosa is lined by simple columnar epithelium and contains crypts of Lieberkuhn and numerous goblet cells. This article will describe the anatomy and histology of the colon, together with its functions.

Key facts about the colon
Parts Ascending, transverse, descending, and sigmoid
Morphological features Semilunar folds, haustra, taenia coli, appendices epiploicae
Blood supply Colic (right, middle, left) and sigmoid arteries
Innervation Superior mesenteric plexus, vagus nerve, inferior mesenteric plexus, pelvic splanchnic nerves
Histology Simple columnar epithelium with crypts of Lieberkuhn and goblet cells

Anatomy

Parts

Structure of the large intestine (overview diagram)

The colon makes up the longest part of the large intestine. It begins from the caecum at the ileocecal valve and ends in the rectum. The colon is about 1.5 meters long and frames the convolute of the small intestine in the abdominal cavity. However it can be shortened and lie quite flexibly in case of an incomplete rotation of the umbilical loop during embryogenesis.

The colon may be subdivided into four parts: ascending, transverse, descending and sigmoid colon. The ascending colon lies secondary retroperitoneally on the right side of the abdominal cavity and moves towards the right colic flexure at the bottom side of the liver. From there the transverse colon runs intraperitoneally towards the spleen forming the left colic flexure. This part is attached to the posterior abdominal wall by the mesocolon and is therefore very flexible.

Beginning at the left colic flexure the descending colon proceeds downwards secondary retroperitoneally at the left abdominal wall and changes over to the S-shaped sigmoid colon in the left iliac fossa. As the sigmoid colon lies intraperitoneally it has a mesocolon as well. This last part of the colon ends in the rectum at the height of S2-S3.

Morphological features

Macroscopically the colon has some distinct morphological features compared to the small intestine. Semilunar folds arise in the inner surface through muscle contractions. These are merely caused functionally and therefore movable. These folds form pouches on the external surface (haustra).

The longitudinal musculature is concentrated in three strong ribbon-like strips (taeniae coli). The mesocolon is attached to the mesocolic taenia and the greater omentum to the omental taenia, whereas the free (or liberal) taenia is unbound and fully visible. Another characteristic feature of the colon is the small sacculations filled with fat formed by the serosa (appendices epiploicae).

Blood supply

Branches of the superior mesenteric artery (right colic artery, middle colic artery and colic branch of ileocolic artery) supply the ascending and transverse colon. The descending and sigmoid colon are supplied by branches of the inferior mesenteric artery (left colic artery and sigmoid arteries). The middle and left colic arteries form the (inconstant) anastomosis of Riolan. The venous blood drains through the correspondent veins into the superior and inferior mesenteric veins.

Innervation

Until the Cannon-Boehm point at the left colic flexure the sympathetic innervation is carried by nerves of the superior mesenteric plexus, while the parasympathetic innervation through the vagus nerve (cranial nerve X). After that point nerves of the inferior mesenteric plexus carry the sympathetic innervation and the pelvic splanchnic nerves the parasympathetic innervation.

More details about the anatomy of the colon are provided below:

Histology

The colon has the typical histological structure as the digestive tube: mucosa, submucosa, muscularis and serosa/adventitia. The mucosa is lined by simple columnar epithelium (lamina epithelialis) with long microvilli. It is covered by a layer of mucus which aids the transport of the feces. The mucosa does not contain villi but many crypts of Lieberkuhn in which numerous goblet cells and enteroendocrine cells are found.

Colon (histological slide)

The connective tissue layer (lamina propriae mucosae) is filled with macrophages, plasma cells and other immune cells. The submucosa comprises blood vessels, lymph nodes and particularly fat tissue. The inner circular musculature of the muscularis is strongly pronounced whereas the outer longitudinal musculature is practically only found in the taeniae.

If you want to test your knowledge about the histology of the colon, tackle the following quiz:

Function

The main task of the colon is the temporary storage and transport of the feces. Thereby it daily absorbs about 1 liter of water which leads to a thickening of the stool. Furthermore it absorbs sodium, potassium and chloride but can also secrete potassium into the lumen itself. The physiological intestinal flora is rich in anaerobic bacteria (approx. 1011/g) which live in symbiosis with the human body. They fulfill essential functions such as decomposing indigestible food ingredients (e.g. cellulose), producing vitamin K, promoting the intestinal peristalsis and supporting the immune system.

Colon and arteries in a cadaver: The splenic flexure located between the transverse and descending colons is a watershed area, which is extremely prone to ischemic injury.

Anatomical features

Macroscopically the colon has some distinct morphological features compared to the small intestine. Semilunar folds arise in the inner surface through muscle contractions. These are merely caused functionally and therefore movable. These folds form pouches on the external surface (haustra).

The longitudinal musculature is concentrated in three strong ribbon-like strips (taeniae coli). The mesocolon is attached to the mesocolic taenia and the greater omentum to the omental taenia, whereas the free (or liberal) taenia is unbound and fully visible. Another characteristic feature of the colon is the small sacculations filled with fat formed by the serosa (appendices epiploicae).

Colon: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 1,232,112 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • D. Drenckhahn/J. Waschke: Taschenbuch Anatomie, 1.Auflage, Urban & Fischer Verlag/Elsevier (2008), S.267-271
  • U. Welsch: Lehrbuch Histologie, 2.Auflage, Urban & Fischer Verlag/Elsevier (2006), S.381-383
  • M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Innere Organe, Thieme Verlag (2009), S.36-37;226-229
  • G. Ackermann et. al.: Medizinische Mikrobiologie – Virologie, 2.Auflage, Urban & Fischer Verlag/Elsevier (2006), S.65

Photo: Flickr / euthman

Author and layout:

  • Achudhan Karunaharamoorthy
  • Christopher A. Becker

Illustrators:

  • Structure of the large intestine (overview diagram) - Begoña Rodriguez
  • Colon and arteries in a cadaver - Prof. Carlos Suárez-Quian
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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